The present application is based on and claims priority under 35 U.S.C xc2xa7119 with respect to Japanese Patent Application No. 2001-088873 filed on Mar. 26, 2001, the entire content of which is incorporated herein by reference.
The present invention generally relates to four wheel drive vehicles (4WD-vehicles). More particularly, the present invention pertains to a differential device for 4WD-vehicles which is capable of selecting any one of a two wheel drive (2WD) state, a differential-free 4WD state, and a differential-locked 4WD state.
A known differential device for 4WD-vehicles is disclosed in Japanese Patent Laid-Open Publication No. Hei.8-85355. This differential device for 4WD-vehicles is capable of selecting any one of a 2WD state, a differential-free 4WD state, and a differential-locked 4WD state. This differential device includes a differential case to which a driving force is transmitted from a driving shaft to rotate, a differential accommodated in the differential case and having a pair of side gears, with the pair of side gears being adapted to deliver the driving force transmitted to the differential case to a pair of wheel axles, a driving shaft adapted to rotate together with one of the road-wheels, and a first sleeve establishing and interrupting a connection between one of the side gears associated with one of the road-wheels and the driving shaft. The first sleeve is operated upon being shifted in position to switch from the 2WD state to the differential-free 4WD state and vice versa. A second shaft is connected to the outer surface of the first sleeve in a spline connection manner, with the second sleeve establishing and interrupting a connection between the driving shaft and the differential case. The second sleeve is operated upon being position shifted to switch from the differential-free 4WD state to the differential-locked 4WD state and vice versa.
However, the above-described known differential device requires a pair of actuators for shifting the positions of the respective first and second sleeves. The need for these two actuators increases the mass and production costs associated with the differential device.
A need thus exists to provide a differential device which is free from the aforementioned drawbacks.
A differential device for 4WD vehicles includes a differential case which receives a driving force from a driving shaft to rotate the differential case, first and second side gears accommodated in the differential case to deliver the driving force transmitted to the differential case at a ratio to first and second wheels, a rotation member rotatable together with the first wheel, a sole actuator, a switching mechanism operably driven in a wheel-axis direction by the sole actuator, and a relative movement inhibiting mechanism. The switching mechanism selectively establishes one of a 2WD state in which the rotation member is out of connection with the first side gear, a differential-free 4WD state in which a connection is established only between the rotation member and the first side gear, and a differential-locked 4WD state in which the first side gear is connected to both the differential case and the rotation member. The switching mechanism includes a movable first member continually connected to the rotation member, with the first member being connected to the first side gear when the first member is moved in one direction along the wheel-axis relative to the rotation member, and with the first member being disconnected from the first side gear when the first member is moved in an opposite direction relative to the rotation member. The switching mechanism also includes a movable second member continually connected to the first member, with the second member being connected to the differential case when the second member is moved in one direction along the wheel-axis relative to the first member, and with the second member being disconnected from the differential case when the second member is moved in an opposite direction along the wheel-axis relative to the first member. The second member is positionable in a first position corresponding to the 2WD state, a second position corresponding to the differential-free 4WD state, and a third position corresponding to the differential-locked 4WD state. The relative movement inhibiting mechanism inhibits on demand movement of the first member relative to the rotation member, and inhibits on demand movement of the second member relative to the first member. The relative movement inhibiting mechanism is constructed so that while the second member is positioned within a range from the first position to the second position, the relative movement inhibiting mechanism inhibits the movement of the second member relative to the first member while the first member and the second member are concurrently moved relative to the rotation member. The relative movement inhibiting mechanism is also constructed so that while the second member is positioned within a range from the second position to the third position, the relative movement inhibiting mechanism inhibits the movement of only the first member relative to the rotation member, while the second member is brought into movement relative to the first member under an immovable condition of the first member along the wheel-axis.
The sole actuator drives the second member to move to the first position, resulting in the 2WD state in which the connection is released between the rotation member and one of the side gears. When the second member is moved to the second position, the first member moves together with the second member resulting in the differential-free 4WD state in which the first member connects the rotation member to only one of the side gears. Moreover, when the second member is further moved to the third position, only the second member is moved, with the first member remaining unchanged in position, thus causing both the second and first members to connect the differential case to the rotation member while also causing the first member to connect the rotation member to one of the side gears. This produces the differential-locked 4WD state in which the rotation member, one of the side gears and the differential case are connected. Thus, a differential is provided in which any one of the 2WD state, the differential-free 4WD state, and the differential-locked state can be selected when the second member is moved to respective positions by driving only the sole actuator, resulting in that the differential device can be down-sized and produced at a lower cost.
It might be possible to integrate the first and second members and drive the resulting member to move to the first, second and third positions to establish the aforementioned driving states. However, when such an integrated member is at its second position at which the rotation member and the side gear are connected by the integrated member, the three members receive a driving torque. Thus, to move the three members to the third position would require movement against the friction force asserted between two adjacent members. Thus, a higher output force is required. In contrast, with the differential here, the second member is moved from the second position to the third position and the second position establishes the connection between the rotation member and the side gear via the first member. Thus, only the second member is moved without having to also move the first member whose sliding friction is relatively large. By making the first member and the second member separate from each other, an excessively high output force of the actuator is not necessary.
The rotation member, the first member, the second member, the first side gear and the differential case are preferably in coaxial alignment with each other, and the second member is preferably a substantially cylindrical member in spline connection with the outer surface of the first member which is also preferably a substantially cylindrical member. In addition, the first member is in spline connection with the outer surface of the rotation member, and the first member is connected to the first side gear in a spline connection. Further, the second member is connected to the differential case in a spline connection. This construction helps facilitate a coaxial arrangement of the rotation member, the first member and the second member, resulting in a downsizing of the differential device so that it occupies minimum amount of space.
The relative movement inhibiting mechanism includes an outer groove formed in the outer surface of the rotation member at a side of the first side gear, a radius-reduced portion formed at the inner surface of the second member and extending in the opposite direction of the differential case from a position on the wheel-axis direction, a snap ring fixed to the end portion of the second member which is near the differential case and capable of engaging a side of the first member which faces the first side gear, and a pin slidably fitted in a radially extending through-hole in the first member. The relative movement inhibiting mechanism is operated so that while the second member is positioned within the range-from the first position to the second position, the inner end of the pin is brought into contact with the outer surface of the rotation member, the outer end of the pin extends from the outer surface of the first member to engage with a shoulder portion of the radius-reduction portion of the second member, and the snap ring is brought into engagement with the side end of the first member. In addition, while the second member is positioned within the range from the second position to the third position, the outer end of the pin is brought into engagement with the radius-reduction portion of the second member, and the inner end of the pin extends from the inner surface of the first member to engage with the outer groove of the rotation member. Thus, the relative movement inhibiting mechanism which forms, together with the first member and the second member, the switching mechanism, can be constructed more easily and at a lower cost.
When the relative movement inhibiting mechanism is requested to integrally move the first member and the second member in the wheel-axis direction when the second member is within the range between the first position and the second position, the radial inner end of the pin is in engagement with the outer surface of the rotation member. This causes the radial outer end of the pin projecting from the outer surface of the first member to engage the shoulder portion of the radius-reduction portion of the second member, resulting in that when the second member moves toward the differential case the first member moves together with the second member. In addition, the engagement between the snap ring and the end of the first member which is at the side of the side gear causes the second member to move together with the first member when the first member moves away from the differential case. Thus, so long as the second member is anywhere in the range between the first position and the second position, the first member always moves in together with the second member.
On the other hand, if the relative movement inhibiting mechanism is requested to integrate the rotation member and the first member in the wheel-axis direction when the second member is within the range between the second position and the third position, the radial outer end of the pin which is in engagement with the radius-reduction portion of the second member causes the radial inner end of the pin to project from the inner surface of the first member to engage with the outer groove of the rotation member. This causes the pin to integrate the first member with the rotation member in the wheel-axis direction, thus making it possible to establish independent movement of only the second member in the wheel-axis direction which is in spline connection with the first member relative to the first member.
Thus, it is possible to change the member which is to be inhibited to establish relative movement depending on whether the radial outer end of the pin which is slidably fitted in the through-hole in the first member projects from the outer surface of the first member while the second member is between the first and second positions or the radial inner end of the pin projects from the inner surface of the first member while the second member is between the second and third positions.
The above described switching of the pin projecting modes (i.e., whether the pin projects from the outer surface of the first member or projects from the inner surface of the first member) is effected when the second member passes through the second position. In more detail, when the sole actuator begins to move the second member from its first position to its second position, the radial inner end of the pin is in engagement with the outer surface of the rotation member. Thus, even if the pin is applied with a component force in the radially inward direction resulting from the engagement between the radial outer end of the pin and the shoulder portion of the radius-reduction portion of the second member, the pin position remains unchanged and is not moved in the radially inward direction (i.e., the pin still projects from the outer surface of the first member), thus establishing an integrated connection between the first member and the second member.
When the second member approaches its second position, the radial inner end of the pin begins to oppose the outer groove of the rotation member and begins to move into the outer groove by the force resulting from the engagement between the radial outer end of the pin and the shoulder portion of the radius-reduction portion of the second member. At a stage when the second member begins to move beyond the second position toward the third position, the radially inward movement of the pin is terminated in its full engagement with the outer groove of the rotation member. Upon completion of such an insertion of the pin into the outer groove, the radial outer end of the pin is no longer in engagement with the shoulder portion of the second member, but with the inner surface of the radius-reduction portion. The pin thus does not move in the radially outward direction. The engagement of the radial inner end of the pin permits relative movement between the first member and the second member, and inhibits relative movement between the rotation member and the first member. As a result, the second member, independent of the first member, moves from its second position to its third position.
When the second member is moved from its third position to its second position, at first the radial outer end of the pin is in engagement with the inside of the radius-reduction portion of the second member so that the pin does not move in the radially outward direction, thereby allowing only the second member to move. During movement of the second member, the connection between the spline portion of the second member and the spline portion of the differential case is released, which results in establishment of the differential-free 4WD state. When the second member reaches its second position, the snap ring fixed to the second sleeve begins to engage the side of the first member which is next to or faces towards the side gear. Simultaneously, the radial outer end of the pin begins to engage the shoulder portion of the radius-reduction portion of the second member(not the inner surface of the radius-reduction portion). Thus, it is possible for the pin to move in the radially outward direction. At this time, the first member moves together with the second member by the force from the snap ring fixed to the second member. With the combination of this force and the tapered groove structure, the pin is applied with a component force in the radially outward direction, thus causing the pin to slide gradually along the shoulder portion in the radially outward direction. At a stage of moving the second member to the first position passing through the second position, the radially outward movement of the pin is terminated and is placed at a position at which the radial outer end of the pin is capable of being engaged with the shoulder portion of the radius-reduction portion of the of the second member. At this time, the radial inner end of the pin is completely out of engagement with the outer groove of the rotation member and is in engagement with the outer surface of the rotation member, thus not allowing the pin to move in the radially inward direction. The radially outward movement of the pin makes it possible to establish relative movement between the first member and the rotation member, and the first member begins to move together with the second member, which is connected to the first member via the snap ring, from the second position to the first position.